Youll see the AVI file has only 10 Audio chunks but 250 video
chunks. That means one audio chunk spans several video frames.
avisplit can not cut a chunk in half, it only handles complete
chunks. If you do, say, avisplit -s 20, it is possible that the first file will
have 6 audio chunks and the second one only 4 meaning there is too much
audio in the first AVI file.

The solution is to remux the AVI file with

transcode -i in.avi -P1 -N 0x1 -y raw -o out.avi

(of course -N 0x1 is not correct for all AVI files).
Now look at tcprobe again

The data in this file is exactly the same (its bit-identical)
as it was in in.avi; the AVI file was just written in a
different way, we do now have 250 audio chunks which makes splitting much
easier and more accurate for avisplit.